This invention relates to improvements in a boring bit, particularly to improvements in tubular nozzles in a boring bit.
During operation, the earliest tubular nozzles and central nozzle in a boring bit are intended to directly inject high speed and high pressure fluid toward the bottom of a borehole while the boring bit is rotating, so as to promote the breaking of touched rock and wash and cool the boring bit, as a result, drilling efficiency is enhanced and bit life is prolonged.
Experiments have proved that the closer the outlet end of a tubular nozzle is to the bottom of a borehole, the higher is the pressure of drilling fluid injected toward the bottom of a borehole, as a result, a higher effect is achieved. Therefore, there has recently been developed a boring bit with extended tubular nozzles of which the lower ends are at a distance substantially equivalent to 2 to 6 nozzle diameters from the bottom of a borehole, which leads to the best result.
U.S. Pat. No. 4,759,415 discloses such a boring bit with extended nozzle tubes. Although its performance is higher than that of the earlier one, however, with a curved region in its nozzle tubes, improvement of bit life is hindered as a result of the fact that high speed and high pressure drilling fluid passing through the curved region deflects fluid, and by violently impinging thereagainst erodes the wall thereof. Furthermore, the curved region increases loss of pressure of drilling fluid and thereby unfavorably influences the enhancing of efficiency.
The object of the invention is to provide a boring bit without the above-mentioned drawback, however with even longer life and higher efficiency.